Eccentrics are used to convert rotary motion into reciprocating linear motion, or vice versa. The amplitude of reciprocation, or throw, may be fixed or variable. In variable throw eccentrics, the adjustment is commonly accomplished by stopping the operation of the device and adjusting the relationship of the parts of the device.
In many applications, it would be desirable to be able to adjust the throw while the eccentric is in motion. In the particular application of metering seed or fertilizer in agricultural seeding implements such as air-seeders, with a suitable metering device a continuously variable throw eccentric drive would allow the rate of application to be varied during operation. In the emerging field of precision farming such desired rates change while passing over various parts of a field. Global positioning systems are used to transmit the precise field location to a computer which can then send the appropriate signal to the metering drive to adjust the rate of application. The metering drives presently used to respond to these signals are expensive and cumbersome.
Similar uses can be seen for metering in other applications such as feed mills, pharmaceutical manufacturing, mines, etc. As well, such a variable throw eccentric could be well utilized in driving shakers, vibrators and the like.
Starting torque requirements could be reduced by an eccentric device which was adjustable in operation. A short throw provides more torque which could be an advantage in start-up, with the throw being gradually increased. The eccentric drive motor could be started with the eccentric in neutral, or zero throw. As the throw is increased, the shaker would gradually attain the desired action. Such a device would act essentially like a clutch. Starting torque requirements often dictate the use of a motor with more power than that required for continuous operation. An example of a conventional variable throw eccentric is described in U.S. Pat. No. 4,249,424.
Conventional eccentric devices are costly and prone to mechanical difficulty.